Locating active structures in the central Nepalese Himalaya: Applications of detrital 40Ar/39Ar thermochronology and cosmogenic radionuclides
Abstract
The southern flank of the High Himalaya corresponds to a sharp transition in landscape morphology that is suggestive of an abrupt change in rock uplift rate. However, sparse geodetic data and a poorly constrained stratigraphy within the Lesser Himalayan metasedimentary sequence allow for multiple interpretations of the neotectonics in this region. Here we integrate detrital 40Ar/39Ar thermochronology and basin-wide cosmogenic radionuclide measurements from small, strike-parallel tributary catchments to delineate breaks in exhumation and erosion history across three trans-Himalayan transects. The 40Ar/39Ar data from these transects establish a regionally consistent trend in which cooling ages to the north of the physiographic transition have been reset during Himalayan orogenesis, while those to the south have remained unreset. South to north gradients in rock uplift rates have therefore persisted at least long enough to preserve a prominent discontinuity in cooling history within the Lesser Himalayan metasediments. While there are some complexities in the pattern of erosion rates revealed by the cosmogenic radionuclides, a fourfold increase in millennial timescale erosion rates coincides with the cooling age break revealed from 40Ar/39Ar thermochronology. This break in erosion rates occurs over less than two kilometers across strike, tightly constraining the locus of active deformation. Using all of the data, the picture that emerges for central Nepal is therefore one in which a system of active, out-of-sequence thrust faults has accommodated differential exhumation over much of the Pliocene-Recent interval. This newly identified fault system is approximately 100 km north of the active thrust front, and is consistent with the hypothesis that spatial patterns of precipitation can exert first-order control on tectonics by controlling the locus of erosional unloading in active orogens.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.H21H..02W
- Keywords:
-
- 1140 Thermochronology;
- 1150 Cosmogenic-nuclide exposure dating (4918);
- 1625 Geomorphology and weathering (0790;
- 1824;
- 1825;
- 1826;
- 1886);
- 8175 Tectonics and landscape evolution;
- 8177 Tectonics and climatic interactions